The invention relates to a method of manufacturing a thin ribbon of magnetic material having a high permeability, excellent flexibility and workability, and consisting essentially of by weight 4-7% of aluminum, 8-11% of silicon and the remainder substantially iron and inevitable impurities and having a compact fine grain crystalline structure without existing substantially an ordered lattice, a thin ribbon thereof, and a magnetic recording and reproducing head made of this thin ribbon.
Since Dr. Hakaru Masumoto has firstly introduced a magnetic alloy consisting of 84.9% of iron, 9.5% of silicon and 5.6% of aluminum in 1936, this magnetic alloy has widely been known as "Sendust" (Trade name). The alloy consisting of this composition ratio shows remarkable soft magnetic characteristics, has almost no magnetostriction nor magnetic anisotropy, and as a result, said alloy has an initial permeability .mu.o of 10.sup.4, coercive force Hc of 0.05 Oe and specific resistance of about 80 .mu..OMEGA. cm, which are excellent characteristics as a soft magnetic material. This alloy is brittle and not flexible and cannot be formed into a thin sheet by rolling, forging or swaging, so that it was used either bulk-like body in a low frequency region or its use is limited to a dust core in a high frequency region.
There was demerit that a fine cracking and chipping inevitably occurred during working and cutting of the ingot to a thin plate of core of the magnetic recording and reproducing head.
At present, this alloy is worthy of merit in magnetic recording technique and recognized as one of excellent magnetic recording and reproducing head materials, because the alloy has the excellent mechanical wear resistance against sliding motion of a magnetic tape, the soft magnetic properties as described above and the high saturation magnetic flux density. Therefore, a plurality of head cores are directly cut out from an ingot of this alloy, even though this alloy is mechanically very hard, about more than 500 of Vickers hardness, and very brittle. If this alloy can be formed into a thin ribbon or thin sheet, it will become more easily workable than the case of handling a bulk thereof and the alloy can be utilized as not only a core material of a magnetic recording and reproducing head but also a wide range usage such as several kinds of induction materials.
An object of the present invention is to provide a method of manufacturing a thin ribbon of magnetic material having a high permeability consisting essentially of by weight 4-7% of aluminum, 8-11% of silicon and the remainder substantially iron and inevitable impurities as a main ingredient and at least one element of less than 7% by weight in total selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Cu, Ti, Mn, Ge, Zr, Sb, Sn, Be, B, Bi, Pb, Y and the rare earth element comprising,
melting said magnetic material at a suitable temperature between a melting point and a temperature not exceeding 300.degree. C. from the melting point, PA1 ejecting the obtained melt onto the cooling substrate having a good wettability suitable under an ejecting pressure of 0.01-1.5 atm. corresponding to the viscosity of the melt, PA1 cooling super-rapidly the melt at suitable cooling rate of 10.sup.3 .degree.-10.sup.6 .degree. C./sec, and PA1 forming a thin ribbon having a compact and fine grain structure and an excellent flexibility and workability.
The other object of the present invention is to provide a method of annealing thus obtained thin ribbon of magnetic material to realize a high permeability without spoiling an excellent flexibility and workability so as to ensure the grain growth and to produce a columnar crystalline structure.
It is known in the Japanese Official Gazette of Patent Laid-Open 138,517/1976 (Kudo et al) a method of producing a thin ribbon by ejecting a melt of magnetic material having a high permeability onto a moving or rotating cooling substrate with high speed such as drum, disc, twin roll or belt conveyor and cooling super-rapidly the melt directly on the surface of the cooling substrate.
This is a method of manufacturing a thin ribbon of magnetic material which comprises melting the magnetic material having Sendust composition, ejecting the melt through nozzle to high speed moving or rotating cooling substrate and super-rapid cooling the melt at a cooling rate of 10.sup.5 .degree. C./sec and forming an amorphous thin ribbon.
It was proposed by the above authors that the thus obtained thin ribbon according to the prior art is durable to apply a cold rolling of several ten %, and annealed by heat treatment after forming to a final configuration of product so as to recover the high permeability of more than 5,000 .mu.o and low coercive force Hc of less than 0.03 by ensuring the grain growth. in the present inventors theoretical analysis, it is very difficult to form an amorphous thin ribbon by super-rapidly cooling the melt having the composition of magnetic material consisting of aluminum 4-7%, silicon 8-11% and the remainder iron, except that the super-rapid cooling at a cooling rate of more than 10.sup.7 .degree. C./sec is necessary to obtain an amorphous thin ribbon in the Sendust composition.
Upon the analytical study, the present inventors found that the super-rapid cooling should be applied at a rate of less than 10.sup.6 .degree. C./sec but more than 10.sup.3 .degree. C./sec so as to obtain a compact, fine crystalline columnar structure perpendicular to ribbon surface distributed without the ordered lattice.
After repeat testing, the inventor found that it is very important to select a suitable measure from the following conditions.
(1) The cooling speed of the melt is preferably selected from 10.sup.3 .degree.-10.sup.6 .degree. C./sec.
(2) The melting temperature of the melt should be determined to a suitable temperature not exceeding 300.degree. C. from the melting point considering with respect to the diameter of nozzle hole and the ejecting pressure.
(3) The viscosity of the melt should be adjusted to a preferable range of 5.5.times.10.sup.-2 .about.3.times.10.sup.-2 dyne.multidot.sec/cm.sup.2 by determining a suitable melting temperature of the melt.
(4) The ejecting pressure of the melt should be selected from a suitable range of 0.01-1.5 atm.
(5) The cooling substrate should be selected from among substrates having good wettability for the melt.
(6) The cooling substrate is preferably held at a temperature between room temperature and 400.degree. C. under vacuum or inert gas atmosphere.
(7) The moving or rotating speed may be preferably adjusted at a high speed so as to adjust the cooling speed of 10.sup.3 .degree.-10.sup.6 .degree. C./sec and obtain a thin ribbon having a compact fine crystalline structure by super-rapid cooling on the moving or rotating surface of a cooling substrate during adhering on the surface of the cooling substrate.
It is very important to select the material of cooling substrate depending upon magnetic material to be used by taking into account a wettability between the melt of magnetic material and the cooling substrate. The wettability is mainly determined by surface tensions of the melt and the substrate. The viscosity of the melt is selected from a suitable range to ensure the good characteristics of spreading the melt without bounding upon the cooling substrate when the melt is ejected through the nozzle. When the melt temperature is more than 300.degree. C. above the melting point, the melt might spread over the cooling surface of the substrate so that the ribbon wafer becomes too thin and some times a greatly notched ribbon similar to a rattan blind might be produced, while when the melt temperature is too low, the jet flow of the melt is not spread and is separated into a number of small particles having irregular configuration. According to the invention, it is preferable to select such a viscosity of the melt that the edges of the melt are made in contact with the substrate at an angle from 10.degree. to 170.degree. with respect to the substrate surface. For this purpose, a temperature of the melt should be selected within the range from the melting point to 300.degree. C. above the melting point, particularly 100.degree. C. to 150.degree. C. above the melting point.
It is also very important that the melt of magnetic material should be instantaneously super-rapidly cooled on the cooling substrate at a suitable cooling rate of at least 1,000.degree. C./sec, preferably 1,000 to 1,000,000.degree. C./sec by taking account of wettability between the melt of magnetic material and the cooling substrate.
According to the invention, it has been found that the pressure under which the melt is ejected through the nozzle should be within the range of 0.01-1.5 atm.
If the ejecting pressure of the melt is too high, a melt would be scattered as the mist or fine particle having irregular configuration or the resulted ribbon becomes a greatly notched ribbon similar to a rattan blind.
The ejection of the melt is preferably effected in a vacuum but it may be carried out in an inert gas or reducing gas atmosphere. Even in the latter case, it is preferable to reduce the pressure.
The invention will be explained in more detail as follows.
Said thin ribbon can be manufactured by said method in the composition of the thin ribbon according to the invention which is substantially the same as that of Sendust alloy, i.e., Al-Si-Fe series base alloy or Sendust series alloy containing suitable subingredient. Therefore, the composition of the thin ribbon according to the present invention is determined to contain by weight 4-7% of aluminum, 8-11% of silicon and the remainder essentially iron and inevitable impurities. However, all elements contained in the conventional Sendust alloy other than the above elements as inhibitor can be contained less than 0.1 wt% in total. Further, less than 60% of iron can be substituted for Ni and/or Co for improving various characteristics in accordance with the purpose, so that nickel and cobalt can be contained in raw material, if necessary.
If these elements are contained more than 0.1 wt% in conventional Sendust alloy, the ribbon manufactured by similar method as prior arts (Japanese Official Gazette of Patent Laid-Open 138,517/1976, 123,314/1977, and 18,422/1978) are brittle and less flexible than that of the ribbon manufactured by the present art disclosed above.
When the contents of aluminum and silicon are out of said range, an initial permeability .mu.o of more than 10.sup.4 and a coercive force Hc of less than 0.1 Oe cannot be obtained, and it is necessary that the contents of aluminum and silicon are determined to 4-7% and 8-11%, respectively.
In the thin ribbon of magnetic material according to the invention, the subingredient added with the main component of 4-7% of aluminum, 8-11% of silicon and the remainder iron may be selected from at least one element of the group consisting of vanadium, niobium, tantalum, chromium, molybdenum, tungsten, copper, titanium, manganese, germanium, zirconium, antimony, tin, beryllium, boron, bismuth, lead, yttrium and rare earth elements in a range of less than 7% in total.
It is observed by our study that the necessary condition for obtaining a thin ribbon having compact fine crystalline structure by super-rapid cooling on high speed moving or rotating cooling substrate the melt having said Sendust composition is to eject the melt by reducing the said inevitable impurities to less than 0.1% in total of carbon, nitrogen, oxygen and sulphur preliminary. The reason is as follows. If the impurities such as carbon, nitrogen, oxygen and sulphur are included in the Sendust alloy in total of less than 0.1%, these impurities have a very low solidability limit, so these impurities cannot be solved in the solid solution of the melt during the super-rapid cooling and these impurities are distributed as a fine precipitation in the matrix of the rapidly cooled thin ribbon. This precipitation is the cause of not only a decrease of bending strength but also the decrease of the magnetic properties. Further, the admixture of oxide in raw magnetic material, particularly dross coupled with fine particle contained in an alloy melt before starting super-rapid cooling becomes a cause of a breakage due to bending in a cooled state of a thin ribbon. Therefore, according to the present invention, a melting and a solidification of melt materials are repeated once or more than once for floating and separating dross or slag on the surface of the melt. It is advantageous to eject the melt having oxide concentration of less than 0.1%.
The material of a moving or rotating cooling substrate or the material of a moving surface at least contact to the ejected melt may be at least one element selected from the group consisting of copper, copper alloy such as beryllium copper alloy, aluminum, aluminum alloy, titanium alloy, steel, alloy steel such as stainless steel, fused silica, fused alumina, etc. by taking account of the composition of the melt and wettability. The melt having the composition of a thin ribbon of magnetic material according to the present invention has better wettability in case of using the cooling substrate made of steel, alloy steel and aluminum or aluminum alloy than that of a cooling substrate made of copper or copper alloy and it is available to super-rapid cooling the melt in a short time. Under the above reason, it is very important that the material of a cooling substrate should be selected by considering the wettability between the melt and the cooling substrate.
It is very important in manufacturing a thin ribbon of magnetic material according to the present invention that raw material should be maintained to high purity, each condition for manufacturing a thin ribbon is suitably selected with respect to material, structure of nozzle and cooling substrate, more specially it is also important in using a cooling substrate to select a mutual pressure applied to the rolls and the roll space and speed and temperature of the rolls to suitable conditions, whereby size of the thus obtained thin ribbon becomes large and high flexibility can be obtained, and also apparent specific gravity considerably becomes close to the real specific gravity and high size precision can be maintained. In this connection, if a temperature of the cooling substrate is maintained uniformly too low in the whole region of producing the thin ribbon in the widthwise direction, the high size precision of thin ribbon cannot be obtained. To avoid this fault, a temperature of twin rolls in the portion of producing the thin ribbon should be maintained up to 400.degree. C. from room temperature by heating. It is a very important factor to elevate magnetic saturation density.
For instance, in case of using a disc as a cooling substrate, if the condition of producing a thin ribbon is rather close to ideal condition, the apparent specific gravity of the thin ribbon becomes low, so that high saturated magnetic density cannot be obtained.
When the temperature of the melt becomes too high, the viscosity is remarkably decreased. When these melts having low viscosity are ejected through nozzle, the melt has a tendency to be in a spherical form by the surface tension. If the ejecting speed is too high, the melt cannot be formed into a continuous jet flow and would be scattered as fine particles by the collision with the air or a turbulent flow in the melt. Each particle is close to the spherical form, and a scattered particle of a large size receives various forces during moving in the air and is greatly modified from the spherical form and rescattered, or particles are agglomerated with each other in some cases. In such a process, if the temperature of said melt is too high, the continuous steady jet flow of the melt cannot be obtained, so that the thus obtained thin ribbon has several unevennesses and its magnetic property is deteriorated.
The other fault in the case of the melting temperature being too high causes two phenomena when the jet flow of melt is stricken to the surface of cooling substrate. In the outset, if the temperature of the melt is too high from the melting point in the collision to the cooling substrate, the jet flow of melt will be repelled on the surface of cooling substrate and scattered as fine particle, the thin ribbon cannot be formed. However, the temperature of cooling substrate is maintained a suitable temperature between room temperature and 400.degree. C., the repellent is not induced, when the viscosity is maintained in a suitable range of 5.5.times.10.sup.-2 .about.3.times.10.sup.-2 dyne.multidot.sec/cm.sup.2, whereby the melt forms a thin ribbon. In the second, when the melt is super-rapidly cooled on the surface of cooling substrate, the free surface of jet flow of melt is not parallel to the moving surface of the cooling substrate. The surface wave is induced by the collision of the jet flow of the melt to the cooling substrate, and unevenness in the thickness of the thin ribbon occurs partially. If the temperature of jet flow of melt is suitably adjusted, the wettability in the contact surface between the melt and cooling substrate is suitably adjusted to fit the surface tension, whereby the surface wave is not resulted, and this is called crystal dumping state. If it is in crystal dumping state, a thin ribbon having a very high size precision can be obtained. If the melt is super-rapidly cooled in the state of oscillating at a high frequency surface wave, and the contact angle between the jet flow of melt and the moving surface of cooling substrate is excessively more than 90.degree. , the solidified thin ribbon becomes like a rattan blind.
It is very important that a flexible thin ribbon is durable to more large pressure to breakage limit than that of brittle thin ribbon. This means that the great working force can be applied to thin ribbon in working.
It is important that the high mass productionability of thin ribbon for using magnetic head can be expected.
It is further observed that the high separation ability for lamination in building magnetic head apparatus can be expected, and it is a significant value that the manufacturing price is reduced.
It is very important that when two thin ribbons are pressed for lamination, a high size precision cannot be expected by brittle thin ribbon. It is worthwhile for actual use not to obtain a flexible thin ribbon. It is necessary to use adhesive agent or aluminum solder to adhere thin ribbons.
In this case, the thermal outer pressure is applied to laminated thin ribbon, the high flexibility of thin ribbon is utmostly requested to manufacture magnetic head means, etc.
It has a high significant industrial value as the flexibility of thin ribbon is high.